package m.shin;
import java.util.Scanner;
public class Con512 {

	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		int x = s.nextInt() , y = s.nextInt();
		int n = s.nextInt();
		int[] a = new int[n];
		for(int i = 0;i < n;i++){
			a[i] = s.nextInt();
		}
		s.close();

		boolean ft = true;
		for(int i = 0;i < n-1;i++){
			if(a[i] * y > a[i+1] * x){
				System.out.println("NO");
				ft = false;
				break;
			}
		}
		if(ft){
			System.out.println("YES");
		}

	}

}